The invention relates to a modular logic construction circuit having input terminals to which one input signal at a time is applied, whereupon there is supplied through its output terminals an output signal which is also dependent upon how the modular circuit was previously set for this purpose via electrical means.
This type of modular circuit has found increasingly wide application as translators, code converters, program storages for the processing of input signals or also as microprogram storages.
It is a known practice to use series-connected combination matrices to obtain specified output signals which are to be derived from specified input signals. As is well known, any logic operation of variables may be represented by the sum of their products or by the product of their sums (cf. "Die Morgansche Gesetze" or "Die Verknupfung von zwei Variablen" in Reiss/Liedl/Spichall: "Integrierte Digitalbausteine", 1970, by Siemens Aktiengesellschaft, Berlin and Munich, p. 34 ff).
Prior art modular circuits that may be utilized for these purposes have such a matrix-type design. In those circuits logic elements are arranged at the intersections of horizontal and vertical lines of a first and a second combination matrix whereby specified horizontal lines can be connected together with specified vertical lines or disconnected from one another.
Modular circuits are found in the prior art wherein "logic elements" may be set to their first or secondary binary state in accordance with a predetermined function table at the fabrication stage by so-called mask programming, cf. MOS/LSI from Texas Instruments, October 1970, by TEXAS INSTRUMENTS INCORPORATED, page 152 ff: "programmable logic arrays", and a Texas Instrument Application Report, Bulletin CA-153, Kent Adres "MOS PROGRAMMABLE LOGIC ARRAYS". However, such modular circuits have the disadvantage that they are made in accordance with customers' specifications, so that high production cost and, hence, high prices per unit will result if small quantities are produced. Another disadvantage is that the predetermined function table of a mask-programmed module cannot be modified.
Another type of modular circuit found in the prior art has electrically-set logic elements. They may be set by the user himself, which results in lower prices in contrast to the aforementioned type, the mask-programmed modular circuits.
A subtype of these electrically-set modular circuits utilizes setting voltages to set the logic elements. Setting voltages, whose magnitudes stand out against normal working voltages, are applied to the input or output terminals, so that the logic elements, energized by excessive currents resulting from the setting voltages, are fused from horizontal or vertical lines. Such modular circuits are designated as "fusible programmable" (cf. SIGNETICS data sheet, OBJECTIVE SPECIFICATION, APRIL 1975: "BIPOLAR FIELD-PROGRAMMABLE LOGIC ARRAY 82S100, 82S101").
Another subtype of these electrically-set modular circuits has specially designed transistors as logic elements. These transistors are driven to the second breakdown when there is a flow of excessive current. This results in transfer of material from their emitter region to their base region. Thus, a diode is formed from a transistor (cf. Intersil, SE Spezial-Elektronic KG, provisional data sheet of January 1975 "ELEKTRISCH PROGRAMMIERBARE LOGIKMATRIX IM 5200").
This type of modular circuit has the disadvantage that, like mask-programmed modular circuits, they can be set only once for a specific function.
Notwithstanding, modular circuits exist in the prior art that can be set any number of times by electrical means, wherein the logic elements are realized at the crossings of horizontal and vertical lines by field-effect transistors having an electrically floating gate. Such electrically floating gates may be charged by applying appropriate setting potentials such that the particular logic elements will not subsequently be driven to their conducting states by subsequently applied control potentials. The inhibiting charging of such electrically floating gates may be canceled by a quenching process.
This type of prior art modular circuit is described in IBM Technical Disclosure Bulletin, Volume 17, No. 10, March 1975. In this arrangement there are provided per storage location, i.e., per crossing of a horizontal and a vertical line, two transistors, viz, one field-effect transistor having an electrically floating gate and one conventional field-effect transistor. By applying appropriate potentials the electrically floating gate of the particular field-effect transistor can be charged or discharged. The second conventional field-effect transistor assigned to the field-effect transistor equipped with the electrically floating gate is provided for switching on or off control circuits for the storage location. Such a modular circuit permits the setting of their storage locations any number of times via electrical means, thereby obviating the disadvantages of the previously described systems.
A disadvantage of this floating gate type modular circuit, however, is that at least two transistors are necessary per crossing of a horizontal and a vertical line of a combination matrix. Moreover, special control terminals must be provided for setting the logic elements having electrically floating gates.
The necessity of using two or more transistors per crossing results in greater circuit-space requirements per logic element and a correspondingly larger power dissipation. Furthermore, the necessity of using special control lead terminals is a disadvantage; the terminals utilized for this purpose can no longer be available for other functions of the module.
It is an object of the present invention to provide a modular circuit which does not exhibit the disadvantages enumerated hereinabove. The circuit-space requirements per crossing of horizontal and vertical lines must be small so as to achieve close packing of the component parts. Furthermore, dissipation must be small so that service life and operational reliability are greater than those provided in prior art systems. Finally, the terminals provided for the operation of the modular circuit must also be utilized for the setting of the logic elements; accordingly, the majority of these module terminals must still be available for other functions of its operation. One object of the invention is that no elements of any kind are necessary between the two series-connected combination matrices so that in addition to good economy of circuit-space and power dissipation it is also possible to provide for an optimum arrangement of conductor paths.